The invention relates generally to print quality control within an ink jet printer. More particularly, the invention relates to adjusting the print quality of an ink jet printer based on the print head temperature and the media type used during printing.
Ink jet printers are becoming much more common as the printer of choice because of their relatively low cost compared to laser printers and the ability of ink jet printers to produce multi-color images on a variety of media types at reasonable costs per printed sheet. Recent improvements in ink jet printers include improvements in the print heads and the ink cartridges and improved or specialized ink formulations. These improvements have led to improved print quality which results in the ability to produce high quality and/or photographic images. As the use of ink jet printers continues to expand, the need to produce images on a variety of print media has also expanded.
For many applications, the type of print media used in an ink jet printer has little effect on the usefulness of the resulting printed product. However, for certain applications, it is important to identify the media being used for the printing operation. That is, ink spread varies depending on the type of media. For example, plain paper allows the ink to wick into the paper fibers which tends to create a larger spot. On the other hand, coated and glossy types of paper tend to keep the ink spot well rounded, not allowing the ink to spread. As a result, spots tend to be smaller on higher quality media than on plain paper for the same ink drop mass. As drop mass increases, spot size also increases. Drop mass can be controlled within limits by adjusting the ink temperature before firing. It is desirable to optimize the spot sizes so that they are substantially the same regardless of the media type used in the printing application.
Ink jet printers have the capability of printing on a variety of media types, from glossy paper to overhead projection media to plain paper. The variety of printable media places a demand on ink jet printer manufacturers and designers to print quality images on the full gamut of media types without losing print quality or speed. As described above, ink spreads differently depending on the media type used in the printer, which makes ink spot size optimization difficult when using media of varying characteristics. Furthermore, ink droplet misdirection may be exacerbated due to the media type used during the printing application. Ink droplet misdirection is a function of the ink temperature which determines the ink drop exit velocity. Faster exiting ink drops tend to be less misdirected when printed.
What is needed, therefore, is a method and apparatus to control ink drop properties based on temperature and media.
The foregoing and other needs are met by a printing apparatus and method for controlling the ink droplet mass of the ink ejected from the nozzles of a printhead in an ink jet printer. The printing apparatus is used for printing a desired image having a spatial resolution onto a print medium. The printing apparatus includes a printhead having a plurality of printing elements for ejecting ink droplets having a mass onto the print medium, and a temperature sensor for sensing a temperature of the printhead and producing a temperature signal. The apparatus also includes a media sensor for determining what type of print medium is loaded in the printer and producing a print medium signal based on the type of print medium installed in the printer. A plurality of heating devices are located adjacent the printhead for adjusting the temperature of the printhead. The apparatus includes a printer controller for receiving the temperature signal from the temperature sensor and the print medium signal from the media sensor, for determining the temperature of the ink based on the print medium signal, and for activating the heating devices to maintain the temperature of the printhead within a desired temperature range that is dependent upon the print medium signal.
In another aspect, the invention provides a method for adjusting the characteristics of ink droplets ejected from an inkjet printhead to form dots on a print medium. The dots printed during multiple passes of the printhead across the print medium form a printed image on the print medium. The method includes sensing a print medium type and sensing a printhead temperature. Moreover, the printer controller determines, based on the print medium type, an optimal temperature range in which to maintain the printhead temperature and maintains the printhead temperature within the optimal temperature range. The image is printed by ejecting the ink droplets from the printhead as the printhead passes across the print medium to form the printed image.